Dust dissemination poses safety, health and environmental problems in many commercial environments. For example, in many industries such as mining, mineral processing, agricultural, power, steel and paper, the transportation handling and storage of bulk solids is common. One major problem associated with the handling of bulk solids is dust generation and the subsequent emission of a dust into the atmosphere.
Industrial sources of fugitive dust include production, open operations, leaks and spills, storage, disposal, transit or poor house keeping of sundry finely divided solid particulates. Mining industries are replete with examples of the above-enumerated categories. For example, coal mining operations encounter dust dissemination during production, transportation, storage and use.
A typical method for controlling or suppressing dust is to apply a water spray. However, water sprays only control dust for a short period of time depending upon environmental conditions. The application of the spray has to be repeated frequently to provide ongoing dust control. Water sprays for dust control on coal can affect the BTU content of the coal due to wetting, as well as cause significant handling problems when temperatures are below freezing.
Various foam treatments have been utilized to control dust emissions. U.S. Pat. No. 3,954,662 discloses aqueous foamable compositions and their use to control coal dust which comprises water, a detergent wetting agent and an interpolymer of a polymarizable vinyl ester and a partial ester component. U.S. Pat. No. 4,400,220 discloses a method and apparatus for supplying foam to a dusty material to prevent dust particles from becoming airborne. The method includes forming a dust suppressing foam by forcing a mixture of air, water and a surfactant through a foam generating apparatus. The foam generating apparatus forms foam of small bubble size by pushing the unfoamed mixture through a myriad of tortuous passages. The foam generating apparatus requires separate sources of foaming agent, water and compressed air, which are mixed just prior to being forced through the foam generating apparatus. The apparatus provides a foam of sufficient quality and bubble size to suppress respirable dust. However, the apparatus requires three separate feed lines to the mixer/foamer, which complicates the system. One feed line is compressed air, which would require an air compressor.
Foam generating apparatus, which employ an air eductor to obviate the need for an air compressor, are used in fire fighting foam generation. U.S. Pat. No. 5,613,773 discloses an apparatus and method for generating foam from a pressurized liquid. The pressurized liquid is water. Passage of the water through an eductor draws in a foam concentrate which is mixed with the water and thereafter generated into foam by passage through an agitator orifice. The air component of the foam is drawn into the foam concentrate/water mixture as it passes through the agitator orifice. The apparatus of U.S. Pat. No. 5,613,773 does not require an air compressor or a separate pressurized air line. However, a separate line is required for the water and the foaming concentrate. Furthermore, the foam generated by the apparatus disclosed in U.S. Pat. No. 5,613,773, suitable fire fighting, is of relatively low quality. That is, foam suitable for fire fighting is relatively "wet" in that it contains a relatively high percentage of water, increasing the amounts of water in the foam decreases the foam expansion ratio. Also, foam suitable for fire fighting has relatively large bubbles and a limited half life due in part to the high percentage of water. The large bubble size and high water content of fire fighting foam makes it unsuitable for dust control use.